The present invention relates to control systems for printers which may be used with computers, word processors and the like and, more particularly, to a control system for a high speed printer of the type in which a carriage carrying a type wheel with type members, type selection mechanism and/or hammering mechanism is moved predetermined distances to successively print out data on a sheet.
Generally, in a high speed impact printer, a type selection mechanism selects desired one of characters, symbols and other types carried on a type wheel. The selected type is pressed against a sheet through an inked ribbon or the like by a hammering mechanism. A carriage having the type wheel, type selection mechanism and/or hammering mechanism mounted thereon is moved a given distance to reproduce data on the sheet. A problem has existed in this type of printer due to hunting which results from the movement of the carriage or "movable printing member" as sometimes called hereinafter. After the carriage has shifted a given distance such as a distance corresponding to one character, it undergoes hunting and oscillates to opposite sides of a predetermined stop position. If the hammering mechanism is driven to reproduce data before the oscillation settles, the actual position on a sheet on which a type impinges becomes dislocated relative to a specified proper position. This results in irregular distribution of spacings along a train of characters on the sheet.
The same problem has also arisen when the type selector mechanism and type wheel on the carriage are to be driven individually to select one type out of various types carried on the type wheel.
A known expedient for overcoming such a problem consists in controlling the printer such that upon the lapse of a predetermined delay time after the movable printing member has completed a shift, the next motion, which is a type selecting motion, printing motion or spacing motion (sometimes termed generally as "printing operation" hereinafter), is initiated.
However, the time period necessary for the movable printing member to regain stability after a shift is not always constant. When the distance the printing member travelled at a time is relatively large as in the case of a tabulated movement, the printing member oscillates so greatly that a substantial time period is consumed before the vibration settles to stabilize the printing member. Even if the amount of a shift of the printing member is very small, oscillation still occurs due to a delay in response at a start of the shift because the velocity of the printing member sharply varies from acceleration to deceleration. This oscillation does not settle soon and, again, a substantial period of time is required before the printing member restores stability.
While such a situation may be coped with by lengthening the delay time after a shift of the printing member, a longer delay time results in a slower printing rate of the printer and, accordingly, a slower data processing rate of the whole system.
Where the delay time after a shift of such a movable printing member is fixed, another problem arises that the alignment of reproduced characters becomes poor. Generally, the amount of a shift of the movable printing member in printing operation depends on the size of characters to be printed out, i.e. the size of types used. Thus, the fixed delay time may be optimum for one size of types but not for another size of types, significantly degrading the alignment of characters reproduced by the latter size of types.